1. Field of the Invention
The present invention relates to a sheet discharging apparatus for use in an image forming apparatus such as an electrophotographic copying machine, a sorter and a printer.
2. Description of the Prior Art
An ADF (automatic document feeder) is employed, for example, for an electrophotographic copying machine. In the ADF, the conveying speed of originals (sheets) is generally high. Since a discharging speed of originals to be discharged from a discharging mechanism of the ADF is also high, the originals are discharged into a mess unless the discharging speed is reduced. The mess is remarkable particularly when the size of the original is small (for example, B5 and A5), since small-size originals are of light weight. As methods of discharging originals from the above-mentioned ADF, etc. into a well-ordered condition so as to improve stocking capability (aligning capability), methods of electrically reducing the discharging speed and methods of mechanically reducing the discharging speed have conventionally been known.
As one of the methods of mechanically reducing the speed, a method is known where a special discharged original stopper, as shown in FIG. 1, consisting of an elastic body 1 and a stopper body 2 is provided on a discharging portion 5 to align originals discharged in the direction of arrow m1. As another method of mechanically reducing the speed, a method is known where a brake member 3 made of a film or a bar is hung, as shown in FIG. 2, from a discharging outlet 6 onto the discharging portion 5 and originals discharged by discharging rollers 4 in the direction of arrow m2 are brought in contact with the rear surface of the brake member 3 to reduce the discharging speed.
In the method employing the stopper shown in FIG. 1, however, the stocking capability deteriorates because of a rebound of originals unless the discharging outlet is arranged at a position higher than the position where the stopper is arranged. On the other hand, in the method employing the brake member 3 shown in FIG. 2, the stocking capability is not stable for some paper sizes unless the distance between the discharging outlet 6 and the stopper 7 is adjustable. Further, for originals of large sizes, since an unnecessary load is imposed thereon by the brake member 3, the originals can be damaged.
Moreover, as electric methods, a method of reducing a discharging speed by reducing a rotation speed of a discharging roller by controlling the discharging speed with a clutch (Japanese laid-open Patent Application No. S62-12564) and a method of reducing the discharging speed of the discharging roller by reducing a rotation speed of a motor which drives the discharging roller (Japanese laid-open Patent Application S62-269853) have conventionally been known. In automatic document conveying apparatuses of the above prior arts, the stocking capability is improved by reducing the discharging speed just before an original is discharged regardless of the size of the original.
In the apparatus of Japanese laid-open Patent Application S62-12564, however, since two driving systems (a gear and a toothed belt) for a high speed and for a low speed, respectively, are required, it is necessary to provide a changeover clutch and a one-way clutch. Consequently, the mechanism is complicated, and a larger space is required due to the increase in size of the apparatus, thereby increasing the cost.
In the apparatus of Japanese laid-open Patent Application S62-269853, since a separate driving motor is required for a discharging portion, the cost of the motor increases. Moreover, if the discharging portion is driven by the same motor that drives another unit (such as a document conveying portion), the conveying speed of the above-mentioned another unit also decreases when the conveying speed of the discharging portion is low. Consequently, the processing speed of original changeover decreases.